The United Nations Security Council has unanimously imposed its toughest sanctions on North Korea, placing a cap on the hermit state’s key coal exports after its defiant nuclear tests.

The new sanctions resolution - which was spearheaded by the United States and came after three months of tough negotiations with fellow veto-wielding council member China - passed by a 15-0 vote.

The resolution demands that North Korea “abandon all nuclear weapons and existing nuclear programs” and takes aim at the state’s exports of coal, its top external revenue source.

Under Resolution 2321, North Korea will be restricted from exporting more than 7.5 million tonnes of coal in 2017, a reduction of 62 per cent from 2015.

Samantha Power, the US ambassador to the United Nations, said the resolution would strip the regime of more than $700 million in hard currency, dramatically reducing the money it can spend on nuclear and ballistic weapons.

Speaking to reporters with her counterparts from US allies South Korea and Japan, she said the move marked “the strongest sanctions regime the Security Council has imposed on any country in more than a generation.”

“So long as the DPRK makes the choice it has made, which is to pursue the path of violations instead of the path of dialogue, we will continue to work to increase the pressure and defend ourselves and allies from this threat,” Power said, referring to the North by its official name, the Democratic People’s Republic of Korea.

“It sends an unequivocal message that the DPRK must cease further provocative actions and comply fully with its international obligations,” said Ban, who has flirted with entering politics in his native South Korea after his term ends in a month.

Ban said he was still committed to “sincere dialogue” to resolve the nuclear issue and stood by calls to provide humanitarian assistance to ease the suffering of ordinary North Koreans.

China is North Korea’s primary ally and one of the few markets for its coal.

Although Beijing has traditionally protected Pyongyang diplomatically, believing that Kim Jong-Un’s regime is preferable to its collapse, it has grown frustrated by the neighbouring state’s defiance.

China’s UN ambassador, Liu Jieyi, reiterated that Beijing “strongly opposes” the North Korean nuclear tests—but also made a veiled criticism of joint exercises between the United States and South Korea.

“Certain parties increase their military presence and scale up military exercises, thus intensifying the confrontation,” he said at the Council. “This situation must be changed as soon as possible,” he said.